1. Technical Field
The present invention generally relates to electric vehicles and, more particularly, to a method and apparatus for breaking high electric current at high electric voltage under load.
2. Discussion
Electric vehicles commonly use a large battery pack for providing power to the motor for propelling the vehicle. The level of current in conventional electric vehicle battery packs is approximately equal to 400 amps at 400 volts. A number of safety features have been incorporated in to modem electric vehicles to minimize the potential of injury to operators, mechanics, and safety technicians from this current. For instance, the battery pack is often isolated within a tub disposed along the underbody of the vehicle to minimize high voltage/high current exposure. Furthermore, automatic electric contactors open up to remove power from the motor and isolate the current within the battery pack when the vehicle key is turned off.
While these safety features are generally effective, there is room for improvement in the art. For instance, it would be desirable to provide a manually operated battery to backup the automatic system for removing power from the motor and isolating it in the battery pack. It would also be desirable to provide a battery disconnect switch which is accessible to operators, mechanics and emergency personnel so that by moving the switch to an "off" position, they may have confidence that all power has been removed from the vehicle. It further is desirable to provide a battery disconnect switch which is easily recognizable as being in a power off state. Moreover, it is desirable to provide a battery disconnect switch which is capable of breaking the conductive path of the high voltage/high current of an electric vehicle under load while minimizing arcing between contact points.
It is generally known that at high levels of current, such as 400 amps, breaking the conductive path and thus the current flow requires quick action so that an arc between contact points does not form. If the conductive path is not broken quickly enough, the air between the contact points is ionized and begins to burn. An arc then forms between the contact points and travels with the contacts as they are separated. The high current will sustain the arc across the gap through the burning ionized air. The temperature in this region may approach 10,000.degree. F., which may severely damage equipment or cause fires.
In a conventional gas burning automobile employing a standard 12 volt system, the level of current is relatively low and known knife-type switches can be effectively utilized to break the current flow under load. To accomplish this, an operator moves a lever from an "on" position to an "off" position to break the conductive path. In this case, the air between the contact points is not ionized and the current does not arc across the gap because the current is relatively low and does not arc as the contact points are separated.
However, conventional knife-type switches cannot break the conductive path in high voltage, high current systems such as the 400 volt/400 amp system of an electric vehicle since they are hand speed sensitive. An operator is physically unable to move the lever from its "on" position to its "off" position quickly enough to prevent the high current from ionizing the air between the contact surfaces. The high current quickly arcs and jumps across the gap.